1. Field of the Invention
The present invention relates to a process of laying and constructing oil- or natural gas-bearing pipelines over permafrost soil or sub-soil and more particularly in polar regions, such as tundra land, and to pipes and pipelines adapted to and useful for placing them on permafrost soil or sub-soil.
2. Description of the Prior Art
Large oil and natural gas reserves are available in the polar regions and especially in the arctic regions. However, to get the existing energy to the market represents tremendous problems. Plans of pipelines have been drawn up and construction thereof has been started, for instance, to move crude oil from the Prudhoe Bay to Valdez, Alaska, a distance of 798 miles. A number of other pipelines has been planned or proposed. Most of these pipelines are installed on pilings above ground. For instance, 400 miles of the Prudhoe Bay-Valdez pipeline "will require 88,000 support columns" as pointed out by DEAN HALE in the article on "Pipeline Activity in Full Swing" in the "Pipeline and Gas Journal" July 1974, pp. 27 et seq. "The mere act of drilling the holes for the pilings (it is not feasible to drive pilings in permafrost) and setting them in place to provide the pipe supports, will be a colossal undertaking, unlike any pipeline ever built." The design and building of foundations in polar regions and especially in tundra lands for oil- and gas-carrying pipelines and other equipment are complicated by the fact that tundra is actually nothing else than a frozen bog, extending to considerable depths, known as permafrost.
Unless specific pressures between the foundation and the soil are kept several times lower than those used even in the softest soils, the ice component of the permafrost flows under the load and the foundation sinks with its equipment.
The cost of foundations designed for these conditions becomes prohibitively high, more than the pipeline itself as every cubic yard of material for the foundations has to be transported frequently over many miles of tundra land.
Digging down through the permafrost layer to get to some rock ledge can sometimes mean hundreds of feet and, with few exceptions, is out of question. Even if practically possible, the cost would be prohibitive. Very deep piling has been used, but it has its complications and again, the weight of materials to be brought to the sites entails high costs.
As to laying the pipeline directly onto the permafrost soil, tests have shown that within a short period of time the pipeline will "melt" its way down and will sag critically, creating prohibitive bending stresses in the pipes, finally leading to catastrophic pipe rupture. Indeed, not only the weight of the pipeline when filled with oil, but also the relatively high temperatures required to pump the oil through the pipeline must be taken into consideration because these factors contribute to sinking of the pipeline.
A method has been proposed wherein the pipeline is carried by a layer of insulating gravel, sometimes combined with plastic foam. Unless enormous quantities of gravel and foam are used requiring costly transportation of the bulk of such kind of support, the permafrost gives way and the pipeline will sink beyond control.
Furthermore, constructing the pipeline in the above described manner requires additional construction of haul roads for moving the large amounts of material and equipment required.